The present invention relates to an electronic component mounting apparatus for recognizing a mark provided at a specific location on a printed circuit board, and mounting an electronic component on the printed circuit board.
As commonly known, an electronic component mounting apparatus for mounting electronic components on a printed circuit board recognizes a mark on the printed circuit board and positions the electronic or other component to be mounted during the mounting operation using, for example, a CCD camera or sensors. An illumination device is used, during object recognition, to emit light onto or near the object and thus illuminate the object.
An example of a conventional illumination device is shown in FIG. 12. This illumination device 50 has a CCD camera 51 for recognizing an object 59, and the camera 51 is located at the top center of a case 57. An illumination source unit 52 comprising a plurality of light sources 53 (such as light bulbs or LEDs) is arranged below the CCD camera 51. An aperture 52a is formed in the middle of the illumination source unit 52 to capture light reflected from the object.
With an illumination device 50 according to this conventional arrangement, a portion of the light emitted from each of the light sources 53 in the illumination source unit 52 irradiates the object 59, and the light reflected therefrom passes through the aperture 52a and is captured by the CCD camera 51, as indicated by solid arrows in FIG. 12. It should be noted that with this conventional illumination device 50, all of the light sources 53 in the illumination source unit 52 are turned on in use, so that light is uniformly emitted to the object 59.
Recently, various materials each having a particular surface condition are used as the electronic components and as a mark on the printed circuit board, and various surface treatments are performed. Thus, various improvements have also been made to the illumination device so that it is possible to satisfactorily recognize a variety of objects having various surface conditions.
FIG. 13 shows an illumination source unit 62 in an illumination device according to another conventional arrangement. In this illumination source unit 62, numerous light sources 63 are arranged in a plurality of circles having different diameters (that is, concentrically) such that light sources 63 on the same circle form a light source group, and the quantity of light can be adjusted for each light source group. The quantity of light from the sources 63 in each circle is then adjusted according to the surface condition of the object so that the optimum illumination is provided for object recognition.
Even with an illumination device unit having an illumination source unit 62 as described above, however, if the quantity of light from the sources 63 chosen to be turned on is not sufficient, the illumination required for object recognition cannot be achieved, and the recognition rate may drop or detection errors may occur.
Furthermore, because all of the light sources 63 are arranged on the same plane and oriented in the same direction, the illumination angle of the light becomes dependent on the directivity of the light sources 63. Thus, it is difficult to achieve sufficient brightness at a desired illumination angle. Because of this, it is conceivable to increase brightness, for example, by increasing the number of light sources 63 or by increasing the quantity of light from each light source 63. This, however, can cause such problems as an increase in current consumption, a drop in the stability of the brightness as a result of heat emitted by the light source, and shortened service life in the light sources 63.
Both the light incidence side and emission side of the light path adjusting member may be divided into a plurality of subareas, each having a different index of refraction, and both light-transmitting surfaces of each subarea are segments of a convex curved surface. The light-emitting surface of each subarea may be formed in the shape of a ground glass surface.
Further, the illumination source unit may comprise a plurality of light sources directed toward each subarea of the light path adjusting member, and the light sources can be selectively turned on. Each of the light sources may emit light with a color complementary to a color of the printed circuit board or mark thereon, and may comprise a plurality of light-emitting elements of different colors.
A first advantage of the electronic component mounting apparatus according to the invention is that the mounting apparatus can emit appropriate illuminating light toward an object, and thus accomplish object recognition and mounting operations satisfactorily, because the apparatus comprises, as a device for recognizing a-mark on a printed circuit board, an illumination device with a light path adjusting member disposed between an illumination source unit for illuminating an object and the object to which the illumination is to be emitted. At least the light incidence side or irradiation side of the light path adjusting member is divided into a plurality of subareas each having a different index of refraction, and thus collects the emitted light on a specific area containing the object by emitting light incident from the illumination source unit at different indexes of refraction.
Further, a second advantage of the electronic component mounting apparatus according to the invention is that illumination light passing each subarea can be gathered toward the center of the irradiated light. This is achieved because at least the light incidence side or irradiation side of the light path adjusting member is divided into a plurality of subareas forming concentric circles, and the index of refraction on the irradiation side of each subarea band decreases as it is closer to the center.
Moreover, a third advantage of the electronic component mounting apparatus according to the invention is that light from the illumination source unit is refracted and directed toward the object at all points on each light-transmitting surface. Therefore, the light can be precisely gathered on the object because the light-transmitting surface of the plural subareas in the light path adjusting member is a segment of a curved surface, the curvature of which differs in each subarea.
Yet further, a fourth advantage of the electronic component mounting apparatus according to the invention is that a significant light-gathering effect can be achieved using refraction on both sides of the light path adjusting member. This is achieved because both the light incidence side and the irradiation side of the light path adjusting member are divided into a plurality of subareas, each having a different index of refraction, and both light-transmitting surfaces of each subarea are segments of a convex curved surface.
Yet further, a fifth advantage of the electronic component mounting apparatus according to the invention is that light from the illumination source unit can be diffused and emitted to a specific area including an object, without dropping the light gathering effect of each light-transmitting surface with a specific index of refractions. This is achieved because the light-emitting surface of each subarea is formed in the shape of a ground glass surface.
Yet further, a sixth advantage of the electronic component mounting apparatus according to the invention is that when the light sources of the illumination source unit are selectively turned on so as to emphasize the contrast between a mark and the printed circuit board forming the background thereto, an even clearer image can be obtained. Furthermore, the accuracy of mark recognition by the apparatus can be improved, because the illumination source unit comprises a plurality of light sources directed toward each subarea of the light path adjusting member, and the light sources can be selectively turned on.
Yet further, a seventh advantage of the electronic component mounting apparatus according to the invention is that the overall illumination source unit can emit the illumination light adjusted to a color complementary to the color of the printed circuit board or mark on the printed circuit board. Therefore, a contrast between the mark and the printed circuit board can thereby be enhanced, an even clearer image can be obtained, and the accuracy of mark recognition by the apparatus can be improved, because each light source can emit light of a color complementary to a color of the printed circuit board or mark thereon.
Yet further, an eighth advantage of the electronic component mounting apparatus according to the invention is that each light source can internally produce a color complementary to the color of the printed circuit board or mark. Illumination of this complementary color can be directly emitted from each light source,.and illumination light free of color irregularities can be emitted, because each light source comprises a plurality of light-emitting elements of different colors. As a result, contrast between a mark and printed circuit board can be reliably enhanced suitably according to the surface condition of any printed circuit board or mark. Furthermore, it is not necessary to provide separate light sources for each color, for example, red, green, and blue, in an illumination source unit comprising such light sources. The number of light sources can therefore be reduced, and reduction in the size and weight of the illumination source unit can thereby be promoted.